Novosibirsk in Siberia is not the first city that comes to mind for high-end audio. But that city did come up in an e-mail from Louis Motek, the driving force behind the LessLoss brand located in Kaunas, Lithuania. In his mail Louis mentioned meeting a special person who happened to demo a very special amplifier while in Kaunas on his way to Latvia. Here’s what Louis reported: "I had never heard a really good amp before. They all sounded electronic to me. How did I compare? I always compared to less. Less wire (shorter and shorter loudspeaker cable) to know what the cables were doing in the mix. Less room (headphones) to know what the room was doing in the mix. Less speaker (full-range electrostatics) to know what the crossovers were doing in the mix. Less electronics (amps without feedback) and so forth. Anyway,
I never found an amp which just didn't sound like anything but the music. Until now."

Louis is a very keen guy with a good ear for—and understanding of—music. To make his chimney smoke, he transcribes and typesets musical scores. The rest of the day (and probably night) he spends developing his LessLoss products. His e-mail had piqued curiosity about this amplifier so we contacted the man who had visited Louis. His name is Andrejs Staltmanis, a born Latvian now residing in Münster, Germany. His company Ultraudio distributes these amplifiers for Europe. After e-mailing Andrejs explaining how our interest was sparked, he called us back. We agreed that German was the most common factor in our respective vocabularies so all further communications relied on that.

Andrejs explained how the amplifier was made by NEM, the Novosibirsk Electronic Manufacturing in—of course—Novosibirsk, Siberia. Novosibirsk is the third largest Russian city and a technology center. With the decline of the military, technology is now harnessed for civilian purposes, one of which is audio. NEM’s designer and head engineer Alexey Burtsev believes in pure simplicity for audio. In his NEM AI-50, the audio signal only passes through a handful of parts. To achieve that, he had to use a lot of steel and copper for transformers. The NEM AI-50 puts a hefty 58 kilos on the scale and delivers around 50wpc.

Andrejs was pleased with our review offer and insisted to deliver the beast himself. Not long afterwards, Andrejs pulled up in front of our house. Seemingly effortlessly he picked up the 58 kilos of amplifier from the boot of his car and placed it on our expectant ASI amplifier shelf. Over coffee Andrejs talked about the special design features of the NEM and his own work on computer audio - like building a huge power supply for a Firewire DAC from Switzerland. For now we had the Russian amplifier defrosting from its 3-hour trip from Münster.

The NEM AI-50 is a hybrid that combines two tubes and eight output transistors. A 6H30Pi driver handles voltage gain and current amplification falls on the solid-state output stage. Between driver tube and four bipolar transistors per channel, the signal crosses an extremely finely tuned interstage transformer. NEM is proud of their knowledge and skills in the transformer field and their IT can pass a linear 4Hz to 80kHz signal with just 0.5% of voltage loss - or 99.5% efficiency according to NEM’s literature.

But there’s more to this amplifier. The 6H30Pi runs off its own power supply consisting of an EZ81-type rectifier tube, a dedicated L-input choke filter and subsequent RC filter. The driver tube’s control grid receives its DC bias current from a battery for ultimate stability. But it gets even better when we examine the output-stage power supply. To avoid limiting bass response and dynamics, the designers put enormous effort into developing the power supply for the output transistors. A big advantage was in-house know-how to roll their own transformers from 0.27mill M4 steel wherever possible.

A standard power supply transformer delivers AC to a rectifier to convert AC to pulsating DC. This pulsation requires filtering to leave a smooth direct current. Especially for audio purposes, the kind of filter employed becomes highly relevant. There are capacitor filters (C-filters) and choke filters (L-filters). All filters have to present a fixed load to the rectifier so it switches on and current flows from the power transformer to the filter and not back again. The filter also stores the load charge for the output transistors while one of the rectifiers is closed and non-conductive. This filter should also isolate the power supply output from AC line noise.

Well-designed and executed PSU filtration is vital to an amplifier’s final performance. With abundant available current, realistic dynamics are possible. The better the noise filtration, the lower the noise floor to increase dynamic range. The rectifier in a power supply is basically a switch which conducts only when there is a positive voltage differential between the transformer output and filter input.

A rectifier is as a diode which cannot conduct for the full duration of a sine wave. It closes at some point to prevent back flow into the transformer. A rectifier then must use more than one diode to process a full wave and not merely one phase half. At the filter’s input, the waveform depends strongly on what the rectifier notices of the filter and what DC load the power supply circuit draws. The filter’s output DC voltage relates directly to the form and amplitude of the voltage waveform the rectifier delivers to the filter’s input. If the DC input won’t properly cope with the current load and fluctuates in response, the power supply is considered poorly regulated.

Think of the power transformer, rectifier and input filter as a triple jet fountain trying to keep a ball aloft. Any variation on one of the jets drops the ball. With any power supply, the first input filter is the most critical. Comparing a choke-based to a capacitor-based input filter sees that the choke-based version generates an almost constant current flow into the filter. If a choke had infinite inductance, it would pass constant DC without remnants of switching noise. With a capacitor-based input filter, while the capacitor charges and current rises, the rectifier diode closes and reopens only when the current drops again. Even though this process is very fast, there are interruptions which choke filters don’t suffer. In a choke filter, critical inductance is the value above which the pulsating current from the rectifier becomes continuous. The value we are looking for here is close to the frequency of the lowest present harmonic.

With an AC line frequency of 50 or 60Hz, the value is either 100 or 120Hz. Behind the choke in the power supply circuit sits a capacitor bank. For the lowest harmonic, the first capacitor which the signal encounters acts like a short circuit to block it. This filters out ripple voltage, the variation in DC output of the power supply due to an incomplete removal of the AC waveform. The higher the voltage (or the smaller the choke), the greater this remnant ripple current. To filter it out, the choke needs to conduct continuously. This wants a DC bias current to prevent the negative ripple peaks from ever reaching zero.